Eye movements are movements of small amplitude (1 to 25 minutes of arc), of very short duration (0.01 seconds (s) to 0.05 s) and that have an angular speed that may be as great as 500 degrees per second (°/s). Video cameras have been used for more than ten years to monitor eye movements and to track them. Analyzing the track of the eye by processing eye data makes it possible to identify eye movements of involuntary nature as constituted by micro-movements of the eye (nystagmus), slow drifts of gaze, blinking, eye movements of a voluntary nature (changing the XY coordinates of the gaze position of the eye on the screen), movement speed, saccade amplitudes, gaze fixes, and the durations thereof, and vergence movements.
Collecting and analyzing eye movements by means of an eye tracker, preceded by necessary calibration in order to determine the XY coordinates of the position of the gaze on the screen, have become very reliable, fast, and accurate. They make it possible in real time to obtain the track followed by the eye when inspecting the content of a screen, in particular to study the amount of attention given to components in a visual scene.
The advantages of eye control, for devices were identified very early (Ware & Mikaelien, “An evaluation of an eye tracker as a device for computer input”, CHI+GI, 1987, Conference Proceedings, SIGHI Bulletin ACM, p. 183-188), for military applications (e.g. Smyth, Bates, Lopez, & Ware, “A comparison of eye-gaze to touch panel and head fixed reticule for helicopter display control”—Proceeding of the 2nd Mid-Atlantic Human Factors Conference, 1994, p. 49 et seq.), for man-machine interactions (e.g. R J K Jacob, “The use of eye movements in human-computer interaction techniques—what you look is what you get”, ACM Transactions on Information Systems 1991, 9(3), pp. 152-169), for remote control (e.g.: project of the “IBM Almaden Research Center”), or for robot control (e.g.: Atienza & Zelinsky, 2003 “Interactive skills using active gaze tracking”, Proceedings of the 5th International Conference on Multimodal Interfaces, Vancouver, Canada, pp. 188-195).
When in operation, in particular for controlling pointing and direction, eye movement is faster than control by moving articles because it is more direct, (work of the “Gaze-based interaction group”).
Thus, a high-resolution camera placed at two meters from a person can track the movements of that person's retina and convert them into eye commands. There already exist:                devices for inputting alphabetical characters by analyzing eye gazes on digital keyboards;        more highly integrated gaze-control devices (managing emails, writing text, such as the “Eye-gaze interaction” project and the “Visuoboard” system); and        devices for analyzing behavior on articles (filmed by camera) coupled with analysis of gaze tracking (Atienza & Zelinsky, 2003).        
All of those devices rely on the principle of analyzing a gaze fixed on a zone of the screen (“location-based interaction”) and of positioning the cursor when a fixed gaze is detected. A command is then given by blinking, by hand (clicking a mouse), or by maintaining a gaze for a long duration, e.g. to perform a zoom or to open a menu, in association with the duration of a gaze (“time-based interaction”).
That principle does not enable continuous control to be provided, as is needed for implementing functions of controlling a real or virtual camera (zooming, camera movements, . . . ).
Eye movements and software for analyzing gaze tracks present three characteristics that explain why eye control has until now been limited to eye commands that do not involve continuous movement of the eye for control purposes. Eye control has relied on icons (“location-based interaction”), on buttons, or on locations that are well defined.
A first characteristic is that the eye senses information but does not produce it. When the eyes form part of a control system, it is necessary to distinguish between actions that amount to sensing information and actions that should be taken as commands. Any failure (producing a command when the user is looking, or considering that the user is looking when in fact the user is seeking to issue a command) makes the control system unreliable and difficult to use. For example, a command may be issued by gazing for a sufficient length of time and then blinking the eyelids.
The second characteristic is that the eyes are continuously in movement (micro-movements such as nystagmuses up to saccades of the eye of various amplitudes). It is therefore necessary to distinguish between what counts as a gaze and what counts as a movement of the eye. All software for analyzing eye data does this by aggregating gaze positions that are close together in space and in time. This thus defines zones that correspond to fixed gazes.
A third characteristic is that the analysis software outputs only gazes that are fixed (in terms of location and duration) and saccades (locating the start, locating the finish, providing the amplitude and the duration). Slow and oriented movements of gaze in some particular direction are ignored by the analysis software.
Whether performed mechanically or under software control, camera control always involves movement, such that it is necessary to control the camera by hand as well as by looking at what is being filmed.
There does not exist any eye movement control system for taking two-dimensional (2D), XY pictures even though such a system would present undeniable advantages. Amongst the advantages, mention can be made of the possibility of hands-free control, and above all of controlling the shooting of an image from the image itself, in which the natural way of inspecting the visual scene is applied to taking pictures thereof. For example, such a device would enable a film director with a viewfinder and a monitor screen to work directly on shooting from a monitor screen of large size. Such a large-sized screen presents three advantages:                greater freedom of movement for the gaze of the operator;        greater accuracy in analyzing the detection of eye movement; and        the operator observing the image at a size that is closer to its final size.        
The idea on which the present invention is based is to use gaze as a control system, in particular for controlling a real or virtual 2D and/or three-dimensional (3D) camera by analyzing slow and oriented movements of gaze.
The invention thus provides a control method based on a controlling eye signal, and it is characterized by the following steps:                detecting at least one slow movement corresponding to an eye movement of at least one eye of an operator;        generating a said eye control signal from at least one detected slow movement; and        producing a command from the eye control signal.        
Advantageously, said slow movement corresponds to a regular angular movement of the eye at an angular speed lying in the range 1°/s to 40°/s, particularly in the range 1°/s to 30°/s, and more particularly in the range 5°/s to 20°/s.
Slow movement may be detected by determining its path, in particular its direction, by means of a calculation method, in particular by means of linear regression.
The detection of a saccade (or fast movement) and/or a fixed gaze may give rise to an interruption in the generation of the control signal.
The eye control signal may be a function (an increasing or decreasing function) of the angular movement of the eye. The eye control signal may represent the position of the eye and/or the speed of the slow movement of the eye and/or its direction. In this way, as soon as a slow movement is detected, all of the parameters of the slow movement can be used for generating a continuous command, its start, and/or its end.
At least one control parameter, e.g. a speed, may be a function of at least one eye movement parameter, e.g. its speed and/or its direction.
By way of example, giving a command may consist in making a selection between options. The options may be organized in a continuum or as discrete values as a function of at least one eye movement parameter. For example, so long as the slow movement continues, the choice remains open, and stopping the slow movement or interrupting it over a duration that is greater than a selected threshold determines the choice.
The beginning and/or the end of a command may be generated by the beginning and/or the end of an eye control signal, or indeed by a command given by voice, by eye, and/or by hand.
In a first variant, the type of control to which the eye control signal is allocated is determined by at least one parameter of the eye movement, e.g. its direction.
In a second variant, the type of control to which the eye control signal is allocated is determined by a command given by voice, by eye, or by hand.
The eye control signal may also be an on/off signal.
The invention is particularly adapted to remotely controlling picture-taking by on-board cameras or by cameras on hinged arm booms that are in very widespread use because of the effect they achieve, remote surveillance cameras, and also performing remote actions involving manipulating tools remotely. When manipulation is to be performed remotely, there are two systems to be controlled by hand: the camera (if it is desired to act on picture-taking) and the controlled instrument. The invention makes it possible to control the camera by gaze and to control the instrument by hand.
The invention applies in particular to controlling at least one real or virtual camera by eye.
The type of control to which the control signal is allocated may for example be starting to shoot and/or changing a zoom and/or adjusting aperture and/or adjusting focusing and/or rotating the camera about its own axis (rolling), and/or moving the camera (“traveling”), and/or (in a stereoscopic system) varying the spacing between the axes and/or varying vergence. The particular command may be determined by giving a command by voice (voice and/or eye control (fixing gaze on an icon, blinking, . . . ) and/or by hand (keyboard, mouse, joystick, etc.) or indeed by an angular movement parameter, e.g. direction).
The method of the invention may be characterized in that it includes a prior training procedure performed by an operator. This procedure is based on:                analyzing eye position data in successive same-duration T time windows, and classifying data sets for each window in at least two classes; namely                    a slow movement class in which a data set comprises sequential data points of values that are close to one another and that are organized in a continuous geometrical pattern, e.g. a segment having a slope; and            otherwise a class of non-slow movements.                        
Depending on the selected mode, the class of non-slow movements comprises two sub-classes:                a fixed gaze sub-class, else an eye saccade sub-class defined in particular by an acceleration peak followed by strong deceleration.        